JP2024514498A - nitrogen gas generator - Google Patents

Abstract

The present invention is directed to a nitrogen gas generator comprising a housing having two ends, an ignition means at one end of the housing and a gas outlet opening at the other end of the housing, a volume of a filter at the outlet opening, and a volume of solid propellant comprising sodium azide, a binder, a coolant and between 1-10% by weight of iron(III) oxide. Between the ignition means and the volume of solid propellant there is an active layer. The active layer comprises between 60-90% by weight of sodium azide, between 1-15% by weight of a binder, between 0.1-10% by weight of a coolant and between 5-30% by weight of iron(III) oxide. The content of iron(III) oxide in the active layer is higher than the content of iron(III) oxide in the solid propellant.

Description

The present invention is directed to a nitrogen gas generator comprising a housing having two ends, an ignition means at one end of the housing, and a gas outlet opening at the other end of the housing, a volume of a filter at the outlet opening, and a volume of solid propellant including sodium azide, a binder and a coolant, and iron (III) oxide, present between the ignition means and the volume of the filter. Nitrogen gas is produced when the solid propellant is combusted.

Such a gas generator is known from Applicants' WO 2014/073970. This publication describes a nitrogen gas generator located within a tubular housing. At one end there is an ignition means, which may be a conventional pyrotechnic igniter. Between these ignition means and the filter, which may be a sand filter, a composition consisting of sodium azide, potassium silicate, iron(III) oxide and lithium fluoride is present as a solid propellant or a nitrogen generating composition. do. When the nitrogen generating composition is ignited at one end, nitrogen gas is formed which flows through the unburned nitrogen generating composition and the sand filter to the outlet opening. Via the outlet opening relatively cool nitrogen gas is released into the environment. Such nitrogen gas generators are advantageously used to protect electrical devices such as computer servers from fire. This is because the relatively cold nitrogen gas will not damage electrical components, such as other equipment or servers, which are in the vicinity of the fire, for example.

US 4,203,787 describes solid propellants, also called nitrogen gas generating compositions, based on sodium azide. According to this publication, successful initiation of combustion of a sodium azide composition requires a sufficient amount of initiator to ensure that sufficient hot combustion products of the initiator contact the exposed sodium azide composition sufficiently to fan a self-sustaining flame front. A potassium boron nitrate-lead azide initiator is described in this publication.

No. 4,817,828 contains 61-68% by weight of sodium azide, 0-5% by weight of sodium nitrate, 0-5% by weight of bentonite, 23-28% by weight of iron oxide and 2-6% by weight of graphite fibers and 1-5% by weight of graphite fibers. A nitrogen gas generator consisting of 2% by weight of fumed silicon dioxide particles is described. The described gunpowder igniter is made of potassium boron nitrate and is preferred since peak pressures can be minimized and thus particle damage can be avoided.

EP0619284 describes a nitrogen gas generator. The solid propellant consists of gamma iron oxide and sodium azide in approximately stoichiometric ratios to each other. More preferably, between about 29 and 40 weight percent gamma iron oxide and between about 71 and 60 weight percent sodium azide are present in such compositions. A preferred igniter may be a conventional igniter as described in US 4,902,036. The igniter includes a squib, such as that present for igniting an enhancer packet containing potassium boron nitrate present in an enclosed space. The conductor conducts current to the squib, thereby igniting the squib and also igniting the enhancer packet. Ignition of the rapidly combustible material provides the threshold energy necessary to ignite the nitrogen gas generating composition.

International Publication No. 2014/073970 U.S. Pat. No. 4,203,787 US Patent No. 4,817,828 European Patent Application Publication No. 0619284 U.S. Pat. No. 4,902,036

A problem with prior art nitrogen gas generators is the reliability of their performance. It is preferable that nitrogen gas generators, especially nitrogen gas generators installed to extinguish fires, do not fail when ignited. However, in practice it may occur that a small percentage of the installed nitrogen generators are not able to generate the optimum amount of nitrogen gas. The present invention relates to a nitrogen gas generator that does not fail on ignition or at least always generates a minimal amount of nitrogen gas.

This is achieved by the nitrogen gas generator below.
a housing having two ends, an ignition means at one end of the housing and a gas outlet opening at the other end of the housing;
a volume filter at the outflow opening;
between 70 and 90% by weight of sodium azide, between 1 and 15% by weight of a binder, between 0.1 and 20% by weight of a coolant, and between the ignition means and the volume of filter. a volume of solid propellant comprising between 1 and 10% by weight of iron(III) oxide;
an active layer is present between the ignition means and a volume of solid propellant, the active layer comprising between 60 and 90% by weight of sodium azide, between 1 and 15% by weight of binder, 0 . between 1 and 10% by weight of a coolant, and between 5 and 30% by weight of iron(III) oxide, the content of iron(III) oxide in the active layer being equal to that of the iron oxide in the solid propellant. Nitrogen gas generator with a higher content of (III).

Applicants have found that when an active layer containing a relatively high iron oxide content is used, a more reliable nitrogen gas generator is obtained. Furthermore, nitrogen gas is generated more quickly. A further advantage is that the sodium azide-containing active layer also generates nitrogen gas, thus increasing the volume of nitrogen gas that can be generated by a single nitrogen gas generator according to the present invention.

The present invention is particularly suitable for gas generators having ignition means including a squib and an enhancer packet. Preferably, the enhancer packet includes potassium boron nitrate, i.e., _KBNO3 . When an active layer is present according to the present invention, it is found that propagation after initiation is enhanced. This improvement has been demonstrated to improve reliability at the same amount of _BKNO3 and even allow a reduction in the amount of _BKNO3 . The nitrogen gas generator according to the present invention can release nitrogen more quickly than a nitrogen generator without an active layer and with a higher content of potassium boron nitrate. This feature is relevant for applications requiring a rapid response to a threat. The use of less potassium boron nitrate is advantageous as it improves safety during manufacturing and improves product safety. A further advantage is that the use of less potassium boron nitrate results in a higher purity of the released nitrogen gas.

A problem with the above systems including squibs and enhancer packets is that special safety precautions must be taken when assembling the nitrogen gas generator due to their explosive properties. A further disadvantage is that special compartments in the nitrogen gas generator must exist for the squib and enhancer packet. For this reason, it may be preferred that the ignition means include an electrically heated initiator, such as a glow plug. The electrically heated initiator is advantageous because it does not require a squib in combination with the potassium boron nitrate enhancer packet. A much simpler and safer assembly of the nitrogen gas generator is therefore possible. Additionally, no special compartment for the enhancer packet containing potassium boron nitrate is required, making the design simpler. A further advantage of not having to use potassium boron nitrate is that when a nitrogen gas generator is used, no or significantly less nitric oxide is formed. A further advantage is that the electrically heated initiator does not cause gas surges or shock waves within the nitrogen gas generator that could damage the gas generator. Such surges or shock waves of gas can occur when squibs and enhancer packets are used as ignition means. The next advantage is that the combination of an electrically heated initiator and an active layer provides a more reliable nitrogen gas generator for operation at lower ambient temperatures, such as -25°C. be.

The electrically heated initiator may be, for example, a glow plug such as those used in self-igniting engines such as diesel engines. One glow plug will be sufficient for many applications. In high reliability applications, such as aviation applications, it may be beneficial to have two glow plugs to achieve a dual or redundant system. Glow plugs are typically designed to be temporarily energized, preferably by electrical resistance heating, to a preselected temperature in the range of 200-1200° C. for a short period of time. The glow plug preferably includes a sheath, advantageously monolithic, having a relatively thin, generally annular wall defining a blind bore, and a heating element disposed within the blind bore and adapted to emit heat. and a heat transfer device preferably adapted to transfer heat from the heating element to the sheath.

The glow plug may have a conventional heating element, preferably at or near its tip, including a metal coil or metal filament enclosed in a heat-resistant metal or ceramic sheath.

The heating element preferably includes at least one or more metal filaments or coils, preferably having a high electrical resistance, such that at least one of the one or more metal filaments or coils heats up rapidly when an electric current is passed through the heating element, thereby rapidly heating the sheath surrounding the heating element. The heating element may further preferably include an insulator to protect the heating element from direct contact with the sheath. The insulator may be formed from any suitable material, preferably a ceramic material.

One or more heating filaments or coils may be protected from direct contact with the sheath, preferably by being enclosed within an insulator, whereby the heating assembly, including both the heating filaments or coils and the insulator, is enclosed within the sheath.

the sheath is selected and configured to minimize failure of the heating element assembly caused by thermal stress, oxidation and/or corrosion, and to avoid any stability or performance issues due to proximity to solid propellants; It can be formed from a preselected material. The sheath may in particular contain copper, lead, iron, nickel, which may evaporate or otherwise migrate and thus form explosive and/or toxic heavy metal azides or other undesirable compounds within the gas generator. It must not contain heavy metals such as silver and mercury. This has the advantage that conventional metal coils or filaments containing alloys of heavy metals can be employed, which would otherwise be unsuitable due to the risks involved in direct contact with the propellant charge. .

The metallic coil or filament of the heating element of the glow plug is connected to a power source. A preferred power source is capable of providing between 10 and 30 volts and between 5 and 20 amps to the glow plug for at least 5 to 20 seconds, so that the sheath of the glow plug is rapidly heated to a steady state operating temperature of at least 200°C, more preferably at least 250°C, more preferably at least 500°C, even more preferably at least 750°C, preferably between 900 and 1200°C, even more preferably between 900 and 1000°C. A particularly preferred electrical source is a battery capable of providing at least 12 volts and at least 10 amps to the glow plug for at least 10 seconds, which can be attached to the gas generator. The actual temperature to be achieved is preferably at least equal to or greater than the autolysis temperature of the active layer. This temperature should be sufficient to ignite the active layer.

When electricity is applied to the metallic coil of the glow plug heating element, the coil heats up due to its electrical resistance, heating the sheath until it glows. By applying only partial power to the glow plug, the glow plug sheath is heated to a temperature significantly lower than its operating temperature, which can then be used to heat the solid propellant surrounding the generator so that the propellant can be immediately started. When full power is applied to the coil of the glow plug heating element, the sheath begins to glow and heats the solid propellant surrounding the generator very significantly. When the portion of the active layer surrounding the glow plug's emitting sheath reaches its decomposition temperature, that portion of the active layer begins to start, combusting other portions of the active layer that are more distant from the glow plug sheath.

Preferably, portions of the active layer, particularly the sodium azide propellant of said layer, begin to activate within 10 seconds, more preferably within 5 seconds, after full power has been applied to the coil of the heating element of the glow plug. be able to. The solid propellant layer itself can be activated within 20 to 90 seconds, more preferably within 30 to 60 seconds, after full power has been applied to the coil of the glow plug's heating element.

Preferably, the glow plug, once started, reaches the desired temperature in less than 5 seconds, more preferably less than 3 seconds, more preferably less than 2 seconds. The amount of power that must be supplied to a glow plug according to the invention to initiate decomposition of the active layer depends on the composition and physical appearance of the layer. Suitably, at least 30 watts of electricity, preferably about 50-100 watts, should usually be sufficient to initiate a controlled, self-sustaining decomposition of the active layer.

The heating element of the glow plug is preferably centrally located within the housing of the gas generator. The heating element of the glow plug is preferably encapsulated by an active layer. More specifically, a sheath surrounding one or more metal filaments or metal coils with high electrical resistance is at least partially encapsulated by the active layer. It can easily be used with commercially available glow plugs.

Solid propellants and active layers are known in the prior art and may include binders and coolants as described in applicant's WO 2014/073970 referenced above.

The solid propellant and the binder contained in the active layer may be the same or different, preferably the same. The binder can be a polytetrazole, preferably an alkaline non-organic binder material, more preferably an alkali metal silicate such as potassium silicate (K ₂ SiO ₃ ). Preferably, the binder is potassium silicate (K ₂ SiO ₃ ) for the solid propellant and active layer.

The solid propellant and the coolant contained in the active layer may be the same or different. Preferred coolants are inorganic salts with a heat capacity of at least 1400 J/K/kg measured at 600 K to provide sufficient cooling. The coolant also has an important function as a slag modifier, helping to keep the slag in place after functionalization of the gas generator. Preferably, the heat capacity of the coolant is at least 1900 J/K/kg. The coolant should be inert so that it does not decompose or react with other components in the generator at the reaction temperature of gas generation. The coolant is selected from LiF, Li ₃ N ₃ , Li ₂ SO ₄ , Li ₂ SiO ₃ or 1 selected from NaCl, NaF, KF, CaF ₂ , Li ₂ B ₂ O ₄ , Li ₂ B ₄ O ₇ More than one type of compound is preferred. From the viewpoint of excellent combination properties as a slag modifier, lithium compounds are more preferred, and LiF is most preferred.

The solid propellant contains between 1 and 10% by weight of iron(III) oxide, preferably between 1 and 5% by weight of iron(III) oxide, and even more preferably between 1 and 4% by weight of iron(III) oxide.

The solid propellant is suitably present as an extrudate or, more preferably, as a tablet. The extrudate or tablet is preferably of uniform size and shape. This ensures that a uniform packing with well-defined voids is present in these extrudates or pellets. The presence of voids is preferred since it provides a flow path for the nitrogen gas, which is first produced by the ignited active layer and then by the solid propellant, and through this void as it exists between the unreacted extrudate or tablets of solid propellant, towards the outlet opening at the other end of the housing. Preferably, the extrudate or tablet of solid propellant is present in a volume of solid propellant having a volume between 25 and ¹⁰⁰⁰ mm3, more preferably between 50 and 500 ^mm3 . The voids between the extrudates or tablets in the volume of solid propellant are suitably between 20 and 75% (volume/volume), more preferably between 40 and 60% (volume/volume) of the total volume taken up by the solid propellant in the housing.

Preferred tablets are preferably bound together. This can be achieved by adding an interparticle binder, such as to a solid propellant tablet, preferably when the tablet is placed within the housing of a nitrogen gas generator. An aqueous solution of K ₂ SiO ₃ with a K ₂ SiO ₃ content between 10 and 30% by weight. Bonding the tablets to each other can maintain their structure over time, i.e. maintain the associated voids, resulting in improved packing that avoids the formation of packing defects such as short cuts and dead zones. Therefore, it is advantageous.

The active layer may be present as a homogenous layer of powder or as layered particles such as extrudates or tablets. For example, the active layer may be a cylindrical tablet with a diameter just allowing placement within the tubular housing.

Preferably, the active layer is present as a homogeneous layer of powder. Even more preferably, such an active layer of homogeneous powder is combined with a volume of solid propellant, preferably present as a tablet. A highly preferred embodiment is when such an active layer of homogeneous powder is combined with a volume of solid propellant present as a tablet, the ignition means comprising a glow plug. Even more preferably, there is a channel through the active layer that fluidly connects the volume of solid propellant and the side of the active layer where the ignition means are also present. Such channels may suitably have a maximum cross-sectional dimension, eg a diameter, of between 5 and 20 mm.

The active layer contains between 60 and 90% by weight of sodium azide, between 1 and 15% by weight of binder, between 0.1 and 10% by weight of coolant, and between 5 and 30% by weight of oxidation agent. Contains iron(III).

The volume ratio between the volume of the active layer and the volume of the solid propellant is between 5:95 and 30:70 (vol/vol). The volume is the volume of space in the housing occupied by the active layer and all solid propellant, including any void space, rather than the space occupied by individual tablets.

The filter can be any intermediate material that allows nitrogen gas to pass and has the thermal capacity to reduce the temperature of the nitrogen gas. Suitable filters are described in WO 2014/073970 cited above and can be activated carbon, sand, zeolite or metal. The volume ratio between the volume of the filter and the volume of the solid propellant is between 20:80 and 60:40 (volume/volume), more preferably between 30:70 and 60:40 (volume/volume).

The housing can have any shape. Preferably, the housing is an elongate housing to allow the combustion front of the solid propellant to travel from one end to the end containing the exit opening. Its cross section can have any shape. The preferred shape is tubular as it provides optimum strength per unit mass of the housing.

The invention is illustrated by the following non-limiting examples.

[Example 1]
A tube having a housing with two ends, an ignition means at one end of the housing, and a gas outlet opening at the other end of the housing, is filled with a layer of solid propellant LE tablets having the composition described in Table 1. The volume of the solid propellant LE tablets was 117 ^mm3 /tablet. The void space of this layer was about 49% (volume/volume). The length of the layer was 168 mm.

A 90 mm layer of sand was present between the layer of solid propellant and the gas outlet opening. On the opposite side there is a 12 mm active layer of TL powder with the composition in Table 1. In this layer there was a small axial channel with a diameter of approximately 12 mm, connecting the igniter and the layer of solid propellant LE tablets. In the active layer, a squib and an enhancer packet containing _KBNO3 particles were present as igniters.

After holding the tube at ambient temperature for several hours, the active layer was ignited and the pressure, temperature and time at which nitrogen was released from the gas generator was measured. The time of maximum pressure at the gas outlet opening was measured. The times at which 75% by weight (T75) and 95% by weight (T95) of the theoretically possible amount of nitrogen gas were released were measured. The results are shown in Table 2.

[Example 2]
Example 1 was repeated, except that HE tablets were used instead of LE tablets. The results are shown in Table 2.

[Example 3]
Example 2 was repeated except that no axial channels were present in the layer of TL powder. The results are shown in Table 2.

[Comparative Experiment A]
Example 2 was repeated except that there was no active layer of TL powder. A squib and an enhancer packet containing _KBNO3 particles were present as an igniter in direct contact with the solid propellant HE tablet. The results are shown in Table 2.

The results in Table 2 show that when an active layer is present, more nitrogen gas is produced and released in a shorter time than when such an active layer is not present.

[Example 4]
Example 2 was repeated three times at ambient conditions and the results are shown in Table 3 (Examples 4a, 4b, 4c). In this table, the conversion rate is also given as % by weight. Conversion is the percentage of nitrogen produced compared to the theoretical maximum possible nitrogen that can be produced based on the available NaN ₃ in the HE tablet and TL powder.

[Comparative experiment B]
Comparative experiment A was repeated three times. In all experiments, propagation failed, resulting in very low conversion. The results are shown in Table 3 as B1, B2, B3, and B4.

The results in Table 3 show that the reproducibility and reliability of the nitrogen gas generator with an active layer is better than the results obtained with a nitrogen gas generator without such an active layer.

[Example 5]
Example 1 was repeated, except that the tube was kept at minus 25 degrees Celsius (-25°C) for several hours before igniting the active layer. The results are shown in Table 4.

[Comparative experiment C]
Comparative Experiment A was repeated except that the tube was maintained at minus twenty-five degrees Celsius (-25 degrees Celsius) for several hours before ignition. The results are shown in Table 4.

[Example 6]
Example 1 was repeated except that the tube was held at 65°C (+65°C) for several hours before igniting the active layer. The results are shown in Table 4.

[Comparative experiment D]
Comparative experiment A was repeated except that the tube was held at 65°C (+65°C) for several hours before ignition. The results are shown in Table 4.

Comparing the results of Example 5 and Experiment C and Example 6 and Experiment D, it can be seen that at cryogenic and high temperatures, the presence of an active layer leads to a much more rapid nitrogen gas flow, as indicated by the shorter T75 and T95. It is shown that this results in the generation of

All generators from Examples 4-6 and Experiments B-D were allowed to cool and were opened under controlled conditions. It was observed that the gas generators with active layers showed better radial conversion which is believed to contribute to the desired more reliable propagation in the axial direction.

[Comparative experiment E]
A small-scale cold gas generator consisting of HE tablets (Table 1) with a 58 gram _N2 generation capacity and a porosity similar to the previous example was started using a standard glow plug. The decomposition reaction started 20 seconds after activation of the glow plug and reached complete decomposition 10 seconds after activation (or 30 seconds after activation of the glow plug).

[Comparative Experiment F]
A second small scale cooling gas generator similar to the apparatus used in experiment E was started using a high velocity, high T glow plug. The decomposition reaction was initiated 7 seconds after activation of the glow plug, and again reached full decomposition 10 seconds after start-up (or 17 seconds after activation of the glow plug).

[Example 7]
In a small-scale generator similar to the apparatus used in Experiment F, 10 wt. % of the HE tablet particles were replaced with a high energy top layer composed of TL powder (Table 1), where the decomposition reaction was initiated 3 seconds after glow plug activation and reached full decomposition 4 seconds after start-up (or 7 seconds after glow plug activation). Example 7 shows that the presence of an active layer results in more than twice as fast start-up and full decomposition as compared to a gas generator initiated by the glow plug and without such an active layer.

Claims (21)

A nitrogen gas generator,
a housing having two ends, ignition means at one end of the housing and a gas outlet opening at the other end of the housing;
a volume filter at the outflow opening;
between 70 and 90% by weight of sodium azide, between 1 and 15% by weight of a binder, between 0.1 and 20% by weight of a coolant, and between the ignition means and the volume of filter. a volume of solid propellant comprising between 1 and 10% by weight of iron(III) oxide;
an active layer is present between the ignition means and a volume of solid propellant, the active layer comprising between 60 and 90% by weight of sodium azide, between 1 and 15% by weight of binder, 0 . between 1 and 10% by weight of a coolant, and between 5 and 30% by weight of iron(III) oxide, the content of iron(III) oxide in the active layer being equal to the iron(III) oxide content in the solid propellant. Nitrogen gas generator with a higher content of (III). The gas generator of claim 1, wherein the solid propellant contains between 1 and 4 weight percent iron (III) oxide. The gas generator according to any one of claims 1 to 2, wherein the content of iron (III) oxide in the active layer is at least twice the content of iron (III) oxide in the solid propellant. The gas generator according to claim 3, wherein the content of iron (III) oxide in the active layer is at least three times the content of iron (III) oxide in the solid propellant. A gas generator according to any one of the preceding claims, wherein the ignition means comprises a squib and an enhancer packet. 6. The gas generator of claim 5, wherein said enhancer packet comprises _KBN03 . A gas generator as claimed in any one of claims 1 to 4, wherein the ignition means includes a glow plug. 8. A gas generator according to claim 7, wherein the glow plug has a heating element encapsulated by an active layer. The gas generator according to any one of claims 1 to 8, wherein the solid propellant and/or the binder in the active layer is composed of a non-organic binder material. 10. A gas generator according to claim 9, wherein the solid propellant and/or the binder in the active layer is comprised of an alkaline non-organic binder material. _11. A gas generator according to claim 10, wherein the binder is potassium silicate ( _K2SiO3 ). A gas generator according to any one of claims 1 to 11, wherein the coolant is LiF. Gas generator according to any one of the preceding claims, wherein the solid propellant is present as a tablet with a volume between 50 and 500 mm ³ . The gas generator of claim 13, wherein the tablets are bonded together. According to any one of claims 13 to 14, wherein the inter-tablet void in the volume of solid propellant is between 40 and 60% (vol/vol) of the total volume occupied by the solid propellant in the housing. Gas generator as described. A gas generator as claimed in any one of claims 13 to 15, wherein the active layer is a homogeneous layer of powder and the ignition means includes a glow plug. The gas generator according to any one of claims 1 to 16, wherein the volume ratio of the volume of the active layer to the volume of the solid propellant is between 5:95 and 30:70 (volume/volume). Gas generation according to any one of claims 1 to 17, wherein the volume ratio of the volume of the filter to the volume of the solid propellant is between 30:70 and 60:40 (volume/volume). vessel. A gas generator as claimed in any one of claims 1 to 18, wherein the housing is a tubular housing. Gas generator according to any one of the preceding claims, wherein there is a channel through the active layer fluidly connecting the volume of solid propellant with the side of the active layer where the ignition means are present. . The gas generator of claim 20, wherein the channel has a maximum cross-sectional dimension between 5 and 20 mm.